Wireless detonating system

ABSTRACT

A detonator system wherein communication between detonators is achieved by using a transmitter coil in one detonator to modulate a magnetic field which is measured by means of a receiver coil in another detonator.

BACKGROUND OF THE INVENTION

This invention relates to a detonating system.

US2008/0041261 relates to a wireless blasting system in which at least two components are adapted to communicate with each other over a short range wireless radio link. Use is made of so-called identification code carriers which are associated with respective detonators. The code carriers are capable of communication with each other and with a blast box.

Communication may be effected using various protocols, such as the Bluetooth protocol which operates at a frequency of about 2,45 gHz.

The specification of the aforementioned application also describes certain problems which are encountered when electronic blasting systems which are interconnected by way of wires are used in diverse sites. The use of a short range, high frequency, wireless radio link is intended to address some of these problems. However, the amplitude of a high frequency radio signal in rock is rapidly attenuated. It is then not feasible to communicate directly with a detonator in a borehole. If the equivalent of an identification code carrier is used on a rock surface then the carrier is exposed to the prevailing environmental conditions and can easily be damaged and thereby rendered useless.

A magnetic signal at a frequency of, say, less than 20 kHz can however penetrate rock and soil without undue attenuation. It is then possible to make use of a transmitting antenna with a relatively large area which is positioned at a suitable protected location and which transmits at a power of several tens of watts communication signals to detonators which have appropriate receivers and which are placed in boreholes in the rock. This approach, which enables the use of the identification code carriers or equivalent devices to be dispensed with, is essentially of a unidirectional nature. Reliable communication links can be established from the transmitter to the various antennas which are associated with the detonators in the boreholes, but due to physical limitations of magnetic field propagation, it is not feasible to transmit from each detonator a signal in the reverse direction, over the same distance, to a receiving antenna which may be the same as a transmitting antenna.

A direct drawback thus is that a one-way communication process does not allow an operator to establish whether all detonators are receiving signals correctly from the transmitter. This means that there is no way of determining whether commands to the detonators from a control mechanism are being properly received. The absence of feedback from a detonator to the control mechanism means that safety and functional requirements are, inevitably, compromised.

Another factor, if a single antenna is used to transmit to all of the detonators in the boreholes, is that the size of the antenna and its power demands may be substantial, particularly if the blast site extends over a large area. Other disadvantages include the practical problem of positioning and deploying a large antenna in an underground situation in which space may be limited and of then protecting the transmitting antenna from damage due to rock displaced in a subsequent blasting process.

An object of the present invention is to address at least to some extent the aforementioned situation.

SUMMARY OF INVENTION

The invention is based on the use of a near-field magnetic induction communication technique in which a transmitter coil in one device is used to modulate a magnetic field which is measured by means of a receiver coil in another device.

The power density of a far-field magnetic transmission attenuates at a rate which is proportional to the inverse of the range to the 2^(nd) power

$\left( \frac{1}{r2} \right)$

or −20 db per decade. By way of contrast a near-field magnetic induction system is designed to contain transmission energy within a localised magnetic field which does not radiate into free space. The power density of a near-field transmission does, however, attenuate at a rate which is proportional to the inverse of the range to the 6th power

$\left( \frac{1}{r6} \right)$

or −60 db per decade. A cross over point between a near-field transmission and a far-field transmission occurs at an approximate distance of (wavelength of operation)/(2π). Utilization of the aforementioned factors means that a relatively low powered transmitter functioning at a frequency of, say, 4 kHz which is associated with a detonator inside a borehole is capable of transmitting a signal through rock over a meaningful distance of say, several, or even tens of, meters.

Against the aforementioned background the invention provides a detonator which includes a transmitter which, when actuated, transmits a first signal at a known, predetermined signal strength, a receiver which in operation, receives said first signal from another detonator which is the same as said detonator and which is displaced by a distance from said detonator, a comparator which compares the strength of the transmitted first signal to the strength of said received first signal, and a processor, responsive to the comparator, operable to provide a measurement of the degree of attenuation of the first signal, is received.

The invention further extends to a detonator system which includes at least a first detonator which is located in a first borehole and which includes a first transmitter and a first receiver and a second detonator which is located in a second borehole and which includes a second transmitter and a second receiver, the first borehole being spaced from the second borehole, wherein the first transmitter is actuable to transmit a first signal at a first signal strength and the second receiver is configured to receive the first signal, the second detonator including a processor to measure the strength of the received first signal and to determine at least from the difference between the strength of the transmitted first signal and the strength of the received first signal a measurement of the attenuation of the first signal as it travels from the first borehole to the second borehole.

Each transmitter and receiver may be adapted to function in the ULF or VLF bands i.e. at a frequency of less than 30 kilohertz and preferably at a frequency of the order of 4 kilohertz. As a signal at this frequency has the capability to travel through rock or soil each receiver and transmitter associated with a respective detonator can be wholly contained within a respective borehole and no part thereof would then be located on, or exposed to, an external rock surface. The likelihood of physical damage due to mining or other operations is therefore substantially eliminated.

The invention also extends to a blasting system which includes control equipment and a plurality of detonators, each detonator being of the aforementioned kind, wherein each detonator, via its respective transmitter and receiver, is adapted to communicate in a two-directional manner with a restricted number of detonators in adjacent boreholes, whereby a signal from the control equipment is relayed in succession via the respective transmitters and receivers of at least some of the plurality of detonators along a plurality of outbound paths to all the plurality of detonators and a signal from any detonator is relayed in succession via the respective transmitters and receivers of at least some of the plurality of detonators along a respective inbound path to the control equipment.

Preferably each outbound path is along a path in which the sum of the degrees of attenuation of the signal between successive boreholes, in which the respective detonators are located and along which the signal is relayed from the control equipment, has a minimal value.

Similarly, each inbound path is along a path in which the sum of the degrees of attenuation of the signal between successive boreholes, in which the respective detonators are located and along which the signal is relayed to the control equipment, which has a minimal value.

Each detonator has a respective unique identifier. Thus each path (inbound and outbound) is precisely specified by the unique identifiers of the associated detonators, and by the sequence, or order, of these identifiers.

An objective in the aforementioned process is to enable a communication path to be determined, which is uniquely associated with a particular detonator, in which the attenuation of a signal to or from that detonator is minimised. If the body of rock in which the boreholes are formed is essentially of the same nature (homogeneous) then this path may be one of a minimum physical distance.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a block diagram representation of a detonator according to the invention; and FIG. 2 is a two-dimensional view of a plurality of detonators which are included in a blasting system which has a mesh network configuration, according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 of the accompanying drawings illustrates in block diagram form a detonator 10 according to the invention.

The detonator 10 includes detonating components 12, of known elements, such as an initiator, a primary explosive and the like. These aspects are not individually shown nor described herein for they are known in the art.

The detonator 10 further includes a timer 14, a memory 16 in which is stored a unique identifier for the detonator, a processor 18, a transmitter 20 which is controlled by the processor 18 and which emits a signal through a custom-designed coil antenna 22, a receiver 24 which is connected to the processor 18 and which is adapted to receive a signal detected by a custom-designed coil antenna 26, and a comparator 28.

A battery 30 is used to power the electronic components in the detonator and to provide energy to the initiator to fire the detonator when required.

In use, the transmitter 20 produces a magnetic field which is transmitted by the antenna 22. The magnetic field is modulated with information output by the processor 18 in order to transmit information from the detonator. Similarly, the receiver 26 is adapted to decode a modulated magnetic field signal which is received by the antenna 26 and to feed information, derived from the demodulation process, to the processor 18. The receiver and transmitter function at a frequency of the order of 4 kHz.

FIG. 2 illustrates a detonator system 34 according to the invention which includes a plurality of boreholes 38 which are drilled in a body of rock in, say, an underground location. The spacings 40 between the boreholes 38, the depth of each borehole, and the position of each borehole, are determined by the application of known principles which are not described herein. Each borehole 38 is charged with an explosive composition 42 and is loaded with at least one detonator 10 of the kind described in connection with FIG. 1. For ease of identification the detonators are labelled A1 to A3, B1 to B3, C1 to C3, D1 to D3, E1 to E3 and F1 to F3.

The detonator system 34 also includes control equipment 50 which is used to establish and measure parameters of the blasting system in accordance with operating and safety techniques. The control equipment 50 is adapted to receive signals from the various detonators and to transmit signals to the various detonators as is described hereinafter.

The control equipment 50 is connected to the detonator A2, referred to herein for ease of identification as a sink detonator, via a physical link 52 such as conductive wires. A signal generated by the control equipment 50 is transmitted via the link 52 to the sink detonator A2. Information carried by this signal is extracted and that information is used to modulate a magnetic signal which is generated by the respective transmitter 20 in the detonator A2. A resulting near-field modulated magnetic signal is then transmitted from the coil antenna 22 of the detonator A2.

As is explained hereinafter it is possible for a signal generated at the control equipment 50 to be transmitted via the mesh network to a particular predetermined detonator and for a signal to be returned from that detonator to the control equipment 50. In each instance the signal is relayed sequentially from one detonator to another and is guided to its particular destination. However, as the energy capability of each battery 30 in each detonator 10 is limited it is important for this signal transfer capability to be implemented in an energy efficient manner.

Assume that the sink detonator A2 transmits a signal which is received by a number of adjacent detonators. In FIG. 2 these adjacent detonators are illustrated at least as the detonators A1, B2 and A3. Referring only to the detonator B2, this detonator contains information, previously loaded in its memory 16, which is based on an accurate measurement of the strength of each signal which might be transmitted by the transmitter 20 in the detonator A2.

The signal from the detonator A2 is received by the receiver 24 in the detonator B2 and the strength of the received signal is measured. The comparator 28 in the detonator B2 compares the strength of the received signal to the strength of the transmitted signal—the latter value is, as stated, known from the relevant data which are stored in the memory 16 of the detonator B2. Due to the attenuating effect of the rock material between the two boreholes in which the detonators A2 and B2 are located, the received signal has a lower strength then the strength of the transmitted signal and, by using an appropriate algorithm which is executed by the processor 18 in the detonator B2, a measure of the degree of attenuation of the signal strength is determined. If the body of rock is essentially homogeneous this technique also provides a measure of the physical distance between the boreholes in which the detonators A2 and B2 are located.

It is also possible for the strength of the transmitted signal to be given by a value which is contained in the transmitted signal.

The signal which is emitted by the detonator A2 is also received by the detonators A1 and A3. In each instance a measurement is determined of the degree of signal attenuation between the borehole of the detonator A2 and the borehole of the respective receiving detonator (A1, A3).

Included in each modulated transmitted signal is the unique identifier of the relevant detonator, taken from the memory 16.

Each detonator 10 which receives a signal then transmits a responsive signal. Referring again by way of example only to the detonator B2 the respective components in the detonator B2 cause the generation of a modulated magnetic signal which is transmitted via the respective coil antenna 22. That transmitted signal carries information identifying the sequential path from the control equipment 50, to the detonator A2, and to the detonator B2, and is received at least by the adjacent detonators C2, B3, A2 and B1. In each instance, a corresponding calculation is made of the extent of signal attenuation between the transmitting borehole and the receiving borehole.

Assume, referring to the detonator B3 (again only by way of example) that the detonator B3, in response to the received signal, emits a modulated magnetic signal of the nature which has been described. That signal is received at least by the adjacent detonators B2, C3 and A3.

The process continues in this manner until each detonator has received a corresponding signal which originated from the control equipment 50. It should be borne in mind that each transmitted signal travels in three dimensions. However, for explanatory purposes herein, signal propagation is described as taking place in two dimensions.

Subsequently, a signal containing data of the respective distance measurement between each adjacent pair of boreholes, together with the identifiers of the respective detonators, is propagated along various paths through the mesh network towards the sink detonator A2 which, in turn, transfers such signal to the control equipment 50.

The control equipment 50 is then capable of establishing a computer representation of the configuration which is shown in FIG. 2 i.e. of the various boreholes and the detonators, the identities of the detonators and the expected extent of signal attenuation between each adjacent pair of boreholes. Through the use of appropriate software the control equipment 50 determines how a signal which is intended for any particular detonator 10, which is identified uniquely by means of its identity number, can be sent through the mesh network of detonators in the most energy-efficient manner i.e. along the shortest path through the body of rock i.e. the path which has the smallest degree of signal attenuation. Additionally, the aforementioned process enables each detonator to establish the identity of each adjacent detonator with which it can communicate in a bi-directional manner.

It is apparent that a signal intended for a particular detonator must carry in the correct sequence the unique identifiers of the detonators which lie on the signal propagation path—this is a requirement for each signal going to, or from, the sink detonator.

Once the routing information has been established it is possible for the control equipment 50 to generate a message that is intended for any particular detonator, as identified by its identity number, and then to transmit an outbound message which is intended only for that detonator. In the return direction a detonator can, for example after carrying out integrity and functional capability tests, generate and transmit an inbound signal to the control equipment 50. In each instance, the signal goes along a predetermined path which is determined primarily by the routing information referred to. The control equipment 50 is then able to verify the integrity of the entire blasting system before initiating a fire signal.

The invention makes it possible for the establishment of an energy efficient, reliable and effective bi-directional communication facility between the control equipment and each detonator. This is achieved without the use of a large area primary antenna of the kind referred to in the preamble hereof. 

1. A detonator which includes a transmitter, a receiver which in operation, receives a said first signal which is transmitted at a first signal strength from another detonator which is the same as said detonator and which is displaced by a distance from said detonator, a comparator which compares the first signal strength to the strength of said received first signal, and a processor, responsive to the comparator, operable to provide a measurement of the degree of attenuation of the received first signal from the difference between the first signal strength and the strength of the received first signal, and wherein a) the first signal strength is given by a value contained in the first signal, or b) the detonator contains information based on a measurement of the first signal strength of the another detonator.
 2. A detonator according to claim 1 wherein the transmitter and receiver are each adapted to function at a frequency of less than 30 kHz.
 3. A detonator according to claim 2 wherein said functioning frequency is 4 kHz.
 4. A detonator system which includes at least a first detonator which is located in a first borehole and which includes a first transmitter and a first receiver and a second detonator, which is the same as the first detonator, which is located in a second borehole and which includes a second transmitter and a second receiver, the first borehole being spaced from the second borehole, wherein the first transmitter is actuable to transmit a first signal at a first signal strength and the second receiver is configured to receive the first signal, the second detonator including a processor to measure the strength of the received first signal and to determine at least from the difference between the strength of the transmitted first signal strength and the strength of the received first signal a measurement of the attenuation of the first signal as it travels from the first borehole to the second borehole, and wherein a) the first signal strength is given by a value contained in the first signal, or b) the second detonator contains information based on a measurement of the first signal strength of the first detonator.
 5. A blasting system which includes control equipment and a plurality of detonators, each detonator being a detonator according to claim 1 and including a unique identifier, and being adapted to communicate in a two-directional manner with a restricted number of detonators in adjacent boreholes, whereby a signal from the control equipment is relayed in succession via the respective transmitters and receivers of at least some of the plurality of detonators along a plurality of outbound paths to all the plurality of detonators and a signal from any detonator is relayed in succession via the respective transmitters and receivers of at least some of the plurality of detonators along a respective inbound path to the control equipment.
 6. A blasting system according to claim 5 wherein each outbound path is along a path in which the sum of the degrees of attenuation of the signal between successive boreholes, in which the respective detonators are located and along which the signal is relayed, has a minimal value.
 7. A blasting system according to claim 5 wherein each inbound path is along a path in which the sum of the degrees of attenuation of the signal between successive boreholes, in which the respective detonators are located and along which the signal is relayed to the control equipment, has a minimal value.
 8. (canceled)
 9. In a detonator system which includes a plurality of boreholes formed in a body of rock and a plurality of detonators which are positioned in respective boreholes, a method of determining a communication path between any two detonators, the method including the steps of transmitting from each of said plurality of detonators a respective unique signal of first signal strength, receiving said unique signal at least at each detonator in each borehole which is adjacent the borehole in which the said transmitting detonator is positioned, determining the degree of attenuation of the first signal strength for each received signal, and determining said communication path between said any two detonators as a path in which the sum of the degrees of attenuation between successive boreholes in which the respective detonators are positioned and along which a signal is relayed has a minimal value, and wherein a) the first signal strength is given by a value contained in said unique signal, or b) each detonator contains information based on a measurement of the first signal strength of said unique signal transmitted by each of the other said plurality of detonators. 